A common display device using a light guide plate has an optical display structure in which light emitted from light-emitting devices such as light-emitting diodes is allowed to be incident on the inside of the light guide plate from a side surface in a bottom surface, an upper surface and the side surface of the light guide plate. The incident light is reflected in the inside of the light guide plate efficiently and is emitted from a display area on the upper surface of the light guide plate. On the bottom surface of the light guide plate, a large number of reflection parts having fine protruding shapes are formed for reflecting or refracting outgoing light efficiently.
When the reflection part having the protruding shape is a conical reflection part 61 or a hemispheric reflection part 62 which protrudes from the bottom surface to the inside of the light guide plate as shown in FIGS. 17A and 17B, light incident from all directions is reflected as outgoing light, therefore, only one pattern is capable of being displayed on one display area of one light guide plate.
Accordingly, when plural patterns are desirable to be displayed on one display area as in game machines such as a pachinko machine or a pachinko slot machine, it is necessary to stack plural number of common light guide plates in which display information is recorded by the protruding shapes of reflection parts 61 or 62. When plural light guide plates are necessary, costs are increased. As space for setting plural light guide plates is also necessary, there is a problem that an apparatus will be increased in size.
In order to solve this problem, a disclosure in which a reflection part 65 having a gentle slope 63 and a steep slope 64 is adopted as the shape of protruding shaped reflection parts as shown in FIG. 17C is disclosed in JP-A-2006-75362 (Patent Literature 1). Behavior of incident light onto the reflection part 65 will be explained with reference to FIGS. 18A and 18B.
On a bottom surface of a light guide plate 66, the reflection part 65 is formed by a method such as cutting a cross section. The reflection part 65 includes the gentle slope 63 and the steep slope 64.
FIG. 18A shows behavior of a light 67 that is incident on the light guide plate 66 from a side where the steep slope 64 exists. The light 67 is transmitted after being refracted on the steep slope 64 and the gentle slope 63, propagating inside the light guide plate 66 again. Accordingly, light incident from the steep slope 64 side is not easily outputted from the light guide plate 66,
FIG. 18B shows behavior of a light 68 that is incident on the light guide plate 66 from a side where the gentle slope 63 exists. The light 68 is totally reflected on the gentle slope 63 and is outputted from an upper surface of the light guide plate 66 as alight 69. Accordingly, light incident from the gentle slope 63 side is easily outputted from the light guide plate 66.
Accordingly, a display device in which two patterns “A” and “B” are recorded on one display area of the light guide plate by an aggregation of such prism shapes will be explained with reference to FIG. 19 and FIGS. 20A, 20B.
Part (a) of FIG. 19 shows a state where the pattern “A” represented by a symbol 71 is recorded by an aggregation of reflection parts 70 on the single light guide plate 66 and the pattern “B” represented by a symbol 72 is recorded by an aggregation of reflection parts 73 on the same display area as the display area where the pattern “A” is displayed.
In the reflection part 70 including the gentle slope 63 and the steep slope 64, the gentle slope 63 faces a side surface 66a of the light guide plate 66. In the reflection part 73 including the gentle slope 63 and the steep slope 64, the gentle slope 63 faces a side surface 66b of the light guide plate 66.
Though two light guide plates 66 are shown side by side in (a) of FIG. 19, they are actually a single light guide plate 66, and two patterns represented by symbols 71 and 72 are recorded in one display area of the light guide plate 66 as shown in (b) of FIG. 19.
When the pattern “A” is displayed, approximately parallel light from light sources 74 is allowed to be incident on the inside of the light guide plate 66 from the side surface 66a as shown in FIG. 20A. When a light 75 from the light sources 74 is reflected on the gentle surface 63 of each reflection part 70, the pattern “A” is displayed. The light 75 is incident on the steep slope 64 of the reflection part 73 and is transmitted after being refracted on the gentle slope 63 of the reflection part 73, propagating inside the light guide plate 66 again, therefore, the pattern “B” is not displayed.
When the pattern “B” is displayed, approximately parallel light from light sources 76 is allowed to be incident on the inside of the light guide plate 66 from the side surface 66b as shown in FIG. 20B. When a light 77 from the light sources 76 is reflected on the gentle surface 63 of each reflection part 73, the pattern “B” is displayed. The light 77 is incident on the steep slope 64 of the reflection part 70 and is transmitted after being refracted on the gentle slope 63 of the reflection part 70, propagating inside the light guide plate 66 again, therefore, the pattern “A” is not displayed.
As the light is incident on the light guide plate 66 from the side surface 66a or 66b in opposite directions, the patterns “A” and “B” can be displayed while switching between these patterns.
FIGS. 21A and 21B show a related-art display device in which directions from which light is incident are not opposite directions as shown in FIG. 19 and FIGS. 20A, 20B but are orthogonal directions. In this display device, lengths of sides from which light is incident differ from each other. Also in the display device, patterns to be displayed are switched according to directions of light incident on the light guide plate 66 by changing the direction of the gentle slope 63 of the reflection part in the same manner explained in FIGS. 20A and 20B. For example, two kinds of reflection parts are arranged so that longitudinal directions are orthogonal to each other, and two kinds of light sources 74 and 78 are arranged with respect to two sides respectively so that directions of light incident from the light sources are orthogonal to longitudinal directions of the two kinds of reflection parts. The pattern “A” represented by the symbol 71 is displayed by the light 75 shown in FIG. 21A, and a pattern “C” represented by a symbol 80 is displayed by a light 79 which is approximately perpendicular to the light 75 as shown in FIG. 21B.